A growing number of stream restoration projects have been undertaken to counteract the adverse effects of stream degradation worldwide. Nevertheless, controversies on the real impacts of stream restoration still exist. The objective of this paper is to review the current knowledge base on the impacts of stream restoration in water quality, hydromorphology and fish/invertebrate community. Based on the database developed in this study, 67% of projects indicated a positive effect of nitrogen reduction following restoration. Hydromorphological improvements were identified almost by all hydromorphological restoration efforts. As fish/invertebrate community require a long time-frame to recover, reaching common ground can therefore be difficult due to different time-frames applied by researchers. Given that restoration studies are usually site- and approach-specific, it is impossible to predict every outcome of a stream restoration project by simply extrapolating the results from one single study. However, finding some robust indicators for which could show the uniform trend following restoration is helpful for evaluating the effectiveness of stream restoration projects. Several future research needs should be highlighted: 1) implement high-resolution data analysis, in particular for water quality; 2) choose robust indicators for restoration project evaluation; and 3) avoid comparison using nearby reference streams.
Stream restoration; Water quality; Hydromorphology; Biotic communities
A nationwide investigation found that among 16% assessments of 3.5 million stream miles in the United States in 2004, 44% of them were identified as impaired or polluted (EPA 2004). Countless streams had highly altered flows or were geomorphically degraded (Filoso and Palmer 2011). Over the last two decades, growing public sensitivity toward environmental degradation and scientific awareness of the ecological and biological importance of water quality and hydromorphological diversity in streams have driven numerous attempts to recover degraded systems (Cooper et al. 1997; Roni et al. 2002). Stream restoration, an effort to reshape “more complex ecosystems from more simple and degraded states” (Jansson, Nilsson, and Malmqvist 2007), is a relatively young science and has been considered as a major enterprise, with most focusing on benthic invertebrates, fish population or geomorphic channel stability in the United States (Gerhard and Reich 2000; Jähnig et al. 2010; Moerke et al. 2004). An average of more than $1 billion a year were spent on stream and river restoration in the US (Bernhardt et al. 2005).
However, early in the 1990s, (1995) stated that many “walking aways” from restoration projects after construction without systematic monitoring forfeited the investment if the project failed and prevented the next generation of projects from benefiting from the effort if the project was successful. For instance, (2003) quantified and summarized pre-restoration data on water quality, pesticides concentrations, chlorophyll a, physical in-stream habitat, and biotic community (fish analysis) from the project on Gypsum Creek in Wichita, Kansas. They indicated a potential improvement of stream water quality, physical habitat, and biotic integrity by stream restoration. However, no further publications on the overall effects of stream restoration have been seen probably due to lack of further funding from the state and local management agencies, or literally no effects at all.
Yet, researchers have been trying to quantify the effects of stream restoration with respect to: i) water quality, ii) hydromorphology, iii) riparian zones connection, iv) in-stream habitat, and v) biotic communities. There were five commonly stated goals in the US based on the National River Restoration Science Synthesis (NRRSS) database (Bernhardt et al. 2005). Controversial voices have still been around debating whether stream restoration is worthwhile or not (Kenney et al. 2012). Each individual study can show important characteristics and combining them, as performed in this review, can help illustrate trends. The objective of this paper was to review the current knowledge base on the impacts of stream restoration in water quality, hydromorphology, and biotic communities and can also identify future research needs.
To date, there has been a substantial amount of publications on stream restoration. A dramatic increase of publications containing keywords, either ‘stream restoration’ or ‘stream restoration effects’, was observed since the 1990s from google scholar searching (include patents) (Fig. 1).
Bernhardt, Emily S, Margaret A Palmer, JD Allan, G Alexander, Katie Barnas, Shane Brooks, J Carr, Stephen Clayton, Cliff Dahm, and Jennifer Follstad-Shah. 2005. “Synthesizing Us River Restoration Efforts.” Journal Article. Science 308 (5722):636–37.
Cooper, Scott D, Leon Barmuta, Orlando Sarnelle, Kim Kratz, and Sebastian Diehl. 1997. “Quantifying Spatial Heterogeneity in Streams.” Journal Article. Journal of the North American Benthological Society 16 (1):174–88.
Davis, Nate M, V Weaver, K Parks, and Michael J Lydy. 2003. “An Assessment of Water Quality, Physical Habitat, and Biological Integrity of an Urban Stream in Wichita, Kansas, Prior to Restoration Improvements (Phase I).” Journal Article. Archives of Environmental Contamination and Toxicology 44 (3):0351–59.
EPA. 2004. “National Water Quality Inventory.” Report. United States Environmental Protection Agency.
Filoso, Solange, and Margaret A Palmer. 2011. “Assessing Stream Restoration Effectiveness at Reducing Nitrogen Export to Downstream Waters.” Journal Article. Ecological Applications 21 (6):1989–2006.
Gerhard, Marc, and Michael Reich. 2000. “Restoration of Streams with Large Wood: Effects of Accumulated and Built‐in Wood on Channel Morphology, Habitat Diversity and Aquatic Fauna.” Journal Article. International Review of Hydrobiology 85 (1):123–37.
Jansson, Roland, Christer Nilsson, and Björn Malmqvist. 2007. “Restoring Freshwater Ecosystems in Riverine Landscapes: The Roles of Connectivity and Recovery Processes.” Journal Article. Freshwater Biology 52 (4):589–96.
Jähnig, Sonja C, Karel Brabec, Andrea Buffagni, Stefania Erba, Armin W Lorenz, Thomas Ofenböck, Piet FM Verdonschot, and Daniel Hering. 2010. “A Comparative Analysis of Restoration Measures and Their Effects on Hydromorphology and Benthic Invertebrates in 26 Central and Southern European Rivers.” Journal Article. Journal of Applied Ecology 47 (3):671–80.
Kenney, Melissa A, Peter R Wilcock, Benjamin F Hobbs, Nicholas E Flores, and Daniela C Martínez. 2012. “Is Urban Stream Restoration Worth It?” Journal Article. JAWRA Journal of the American Water Resources Association 48 (3):603–15.
Kondolf, G Mathias, and Elisabeth R Micheli. 1995. “Evaluating Stream Restoration Projects.” Journal Article. Environmental Management 19 (1):1–15.
Moerke, Ashley H, Kerry J Gerard, Jo A Latimore, Ronald A Hellenthal, and Gary A Lamberti. 2004. “Restoration of an Indiana, Usa, Stream: Bridging the Gap Between Basic and Applied Lotic Ecology.” Journal Article. Journal of the North American Benthological Society 23 (3):647–60.
Roni, Philip, Timothy J Beechie, Robert E Bilby, Frank E Leonetti, Michael M Pollock, and George R Pess. 2002. “A Review of Stream Restoration Techniques and a Hierarchical Strategy for Prioritizing Restoration in Pacific Northwest Watersheds.” Journal Article. North American Journal of Fisheries Management 22 (1):1–20.